Update: I took a photo of the ductwork installers phone number and i’m going to call them to get the exact answer.
There is a stove and range hood in basement.
The furnace is not high efficiency, the furnace room is not sealed - no door , and I don’t have pics from down there.
I see it was part of the new ducting system, but what is the purpose?
maybe it is incomplete work?
Would it make sense to get make up air from an attic space? not to me!
ON SECOND THOUGHT,* if it is combustion air and being burned up, then it doesn’t matter if there is insulation dust in it, However, maybe over a long period of time that maybe leave some kinda residue in furnace?
Starting to lean towards it being a combustion air source- makes more sense because in winter, the attic should be as cold as outdoors, and as long as roof is ventilated well its all good.